Antenna device

ABSTRACT

An antenna device for a portable electronic device and an electronic device provided with such an antenna are disclosed. The antenna device is configured to provide in a combination a tuning element for tuning at least one electrical dimension of the portable electronic device and an antenna radiator element of the portable electronic device.

RELATED APPLICATION

This application was originally filed as and claims priority to PCTApplication No. PCT/IB2006/004186 filed 21 Dec. 2006.

The present invention relates to an antenna device and in particular toan antenna device configuration for a wireless communications device.

A communication device can be understood as a device provided withappropriate communication and control capabilities for enabling usethereof for communication with others parties. The communication maycomprise, for example, communication of voice, electronic mail (email),text messages, data, multimedia and so on. A communication devicetypically enables a user of the device to receive and transmitcommunication via a communication system and can thus be used foraccessing various applications.

A communication system is a facility which facilitates the communicationbetween two or more entities such as the communication devices, networkentities and other nodes. An appropriate access system allows thecommunication device to access to the communication system. An access tothe communications system may be provided by means of a fixed line orwireless communication interface, or a combination of these.

Communication systems providing wireless access typically enable atleast some mobility for the users thereof. Examples of these includecellular wireless communications systems where the access is provided bymeans of access entities called cells. Other examples of wireless accesstechnologies include different wireless local area networks (WLANs) andsatellite based communication systems.

A typical feature of the modern mobile communication devices is thatthey are portable, usually small enough to be pocket sized. A modernportable communication device, for example a mobile phone, is alreadyrelatively small in size, but the market is demanding ever smallerportable devices.

A wireless communication system typically operates in accordance with awireless standard and/or with a set of specifications which set outvarious aspects of the wireless interface. For example, the standard orspecification may define if the user, or more precisely user equipment,is provided with a circuit switched bearer or a packet switched bearer,or both. Communication protocols and/or parameters which should be usedfor the wireless connection are also typically defined. For example, thefrequency band or bands to be used for the communications are typicallydefined.

A portable communication device may be provided with so calledmulti-radio capabilities. That is, a portable device may be used forcommunication via a plurality of different wireless interfaces. Anexample of such device is a multi-mode cellular phone, for example acellular phone that may communicate in at least two of the GSM (GlobalSystem for Mobile) frequency bands 850, 900, 1800 and 1900 MHz or acellular phone that may communicate based on at least two differentstandards, say the GSM and a CDMA (Code Division Multiple Access) and/orWCDMA (Wideband CDMA) based systems such as the UMTS (Universal MobileTelecommunications System). A mobile or portable device may also beconfigured for communication via at least one cellular system and atleast one non-cellular system. Non-limiting examples of the latterinclude short range radio links such as the Bluetooth™, various wirelesslocal area networks (WLAN), local systems based on the Digital VideoBroadcasting via Handheld Terminals (DVB-H) and ultra wide band (UWB)and so on.

Since the multi-radio devices communicate over a plurality of differentfrequency bands, a single antenna may not always be best suited for allof the frequencies. Several antennas operating in different frequencybands may thus be needed in a multi-radio antenna system. Regardless thenumber, each of the antennas should provide a good performance. Thismight be required in particular when small mobile devices are concerned.The size of terminals is shrinking at the same time as new services andradio systems are introduced. As a consequence, a need exists for makingthe individual antennas even smaller and minimizing the total volumerequired by the entire multi-radio antenna system of the device.

The metallic chassis, printed wiring board or another element thatprovides what is known as the ground plane of a portable device orterminal has also a role in antenna characteristics of the device. Atfrequencies below 1 GHz the chassis usually provides the major radiatingelement. The chassis also has a role in frequencies above 1 GHz,although usually to a lesser extent.

The chassis and/or printed wiring board (PWB) dimensions and geometrydictate the resonance frequencies of the resonance modes of the mobiledevice. From the impedance bandwidth (BW) point of view, optimaloperating conditions may be achieved when the resonant frequency of thechassis is substantially close to the resonant frequency of the antennaelement.

The joint impedance bandwidth of an antenna and a chassis depends onwhat is known as the effective electrical length of the chassis. Amaximum bandwidth can typically be obtained when the effective length ofthe chassis is a multiple of approximately 0.5λ₀ at the operatingfrequency.

In a typical portable device the physical length of the chassis isnon-optimal when considering the operation of antennas, both cellularand non-cellular. For example, in a monoblock design the chassis may betoo short for a particular frequency band. In a foldable or otherwiseextendable design the chassis may be too long, again depending on thefrequency band.

Recently, some techniques have been introduced for controlling theelectrical dimensions of a chassis, such as the length and/or width ofthe chassis to achieve a more optimal exploitation of the chassisresonance modes. Terminal antenna performance can be significantlyimproved by better exploitation of the chassis resonance modes. Forexample, the bandwidth can be increased by tuning the chassis resonancemodes more optimally by advanced design of the chassis. Instead ofincreasing the bandwidth, the dimensions of an antenna element can bereduced. The techniques for tuning the electrical size of a chassis of acellular phone include, for example, a chassis tuning element. Such anelement is provided by means of a slot in the chassis, a chassis choke(also known as a wave trap), or a chassis loading element. A chassistuning slot or a loading element can be used to increase the electricallength of the chassis in certain selected frequency band(s). A chassischoke can be used to shorten the electrical length of the chassis atsome selected frequencies. The sole functionality of a chassis tuningelement (CTE) has been the tuning of the electrical length of thechassis.

A common problem of the above described techniques to improve theantenna performance is that the implementation thereof requires space,either inside or outside the chassis. In small devices there may not beenough space available for implementing such chassis electrical sizetuning elements.

The herein disclosed embodiments aim to address one or more of the aboveissues.

In accordance with an embodiment there is provided an antenna device fora portable electronic device, wherein the antenna device is configuredto provide in a combination a tuning element for tuning at least oneelectrical dimension of the portable electronic device and an antennaradiator element of the portable electronic device.

Another embodiment provides a portable electronic device comprising suchan antenna device.

A still another embodiment provides a method in a portable electronicdevice, the method comprising tuning at least one electrical dimensionof the portable electronic device by a combined tuning and antennaradiator device and communicating radio signals via the tuned portableelectronic device.

In a more specific embodiment, the tuning element is configured to tuneat least one electrical dimension of a ground plane of the portableelectronic device. The ground plane may comprise a printed wiring boardand/or at least one layer of a multilayer printed wiring board. Theground plane may be embedded in a cover of the portable electronicdevice or may be provided as a part of the housing of the portableelectronic device.

The tuning element may be configured to tune the at least one electricaldimension of the portable electronic device so that the resonancethereof is substantially optimal on at least one given frequency.

The antenna device may comprise at least one separator for separatingthe functions of the tuning element and the antenna radiator element.The at least one separator may comprise at least one of at least onefilter and at least one radio frequency switch.

The tuning element may comprise at least one slot, least one wavetrap,at least one grounded microwave element, and/or at least one loadingelement.

The at least one electrical dimension may comprise at least one of anelectrical length and electrical width.

The antenna device may comprise at least two chokes. The length and/orshape of the at least two chokes may be different. Lumped inductors withdifferent inductor values may be provided within the at least twochokes.

At least one shorting point may be provided for the tuning element andthe antenna radiator element. Separate shorting points may be providedfor the tuning element

For a better understanding of the present invention and how the same maybe carried into effect, reference will now be made by way of exampleonly to the accompanying drawings in which:

FIGS. 1, 2 a and 2 b show examples of wireless communication devices;

FIG. 3 is a flowchart in accordance with an embodiment

FIG. 4 presents an example of a tuning element;

FIG. 5 presents an example of a tuning element in accordance with anembodiment;

FIG. 6 presents a detail of the FIG. 5 device;

FIGS. 7 to 11 present further examples;

FIG. 12 presents an S-parameters magnitude curve for a conventionalprior art antenna;

FIG. 13 presents an S-parameters magnitude curve for an antenna devicein accordance with the embodiment shown in FIG. 5; and

FIG. 14 presents an S-parameters magnitude curve for a high frequencyband antenna; and

Before explaining in detail certain exemplifying embodiments, certaingeneral principles of wireless communication devices are brieflyexplained with reference to FIGS. 1, 2 a and 2 b. A portablecommunication device can be used for accessing various services and/orapplications via a wireless or radio interface. A portable wirelessdevice can typically communicate wirelessly via at least one basestation or similar wireless transmitter and/or receiver node or directlywith another communication device. A portable device may have one ormore radio channels open at the same time and may have communicationconnections with more than one other parties. A portable communicationdevice may be provided by any device capable of at least sending orreceiving radio signals. Non-limiting examples include a mobile station(MS), a portable computer provided with a wireless interface card orother wireless interface facility, personal data assistant (PDA)provided with wireless communication capabilities, or any combinationsof these or the like.

FIG. 1 shows a schematic partially sectioned view of a portableelectronic device 1 that can be used for communication via at least onewireless interface. The electronic device 1 of FIG. 1 can be used forvarious tasks such as making and receiving phone calls, for receivingand sending data from and to a data network and for experiencing, forexample, multimedia or other content. The device 1 may also communicateover short range radio links such as a Bluetooth™ link. The device 1 maycommunicate via an appropriate radio interface arrangement of the mobiledevice. The interface arrangement typically comprises an antennaradiator element. The antenna may be arranged internally or externallyto the device. Possible antenna devices will be described in more detaillater in this description.

A portable communication device is typically also provided with at leastone data processing entity 3 and at least one memory 4 for use in tasksit is designed to perform. The data processing and storage entities canbe provided on an appropriate circuit board and/or in chipsets. Thisfeature is denoted by reference 6. The user may control the operation ofthe device 1 by means of a suitable user interface such as key pad 2,voice commands, touch sensitive screen or pad, combinations thereof orthe like. A display 5, a speaker and a microphone are also typicallyprovided. Furthermore, a wireless portable device may compriseappropriate connectors (either wired or wireless) to other devicesand/or for connecting external accessories, for example hands-freeequipment, thereto.

The device 1 may also be enabled to communicate on a number of differentsystem and frequency bands. This capability is illustrated in FIG. 1 bythe two wireless signals 11 and 21.

FIG. 1 shows a monoblock wireless device. FIGS. 2 a and 2 b showschematic examples of portable electronic devices where the lengththereof can be varied. More particularly, FIG. 2 a shows a foldableportable device 1 and FIG. 2 b shows a portable electronic device 1 thatis extendable between at least two lengths in a sliding or rotatingfashion. As shown, the various sections 7 and 8 of the portable device 1can be electrically connected at 9 regardless the state of extensionthereof.

A portable communication device may be provided with a tuning elementfor tuning at least one electrical dimension of a portable electronicdevice. The electronic dimension may be the length and/or width ofresonating element, a chassis or a ground plane of the electronicdevice.

In the examples shown in FIGS. 4 to 11 and described below the tuningelement is referred by the term chassis tuning element (CTE). Thechassis: tuning element may be provided e.g. by a wave trap, a chassisloading element, or a slot in the chassis. An example of the wave trapis a grounded microwave element. It is noted that although the termtuning element is used in here, this is intended to equally coverarrangements where no particular component is provided but the tuningelement is provided for example by means of a slot.

Conventionally a basic function of a tuning element is to tune theelectrical length of the chassis so that one or more of its resonancemodes will move in frequency domain close to one or more of the operatedfrequency bands. For example, in a cellular device the tuning may beused to provide chassis resonance modes approximately in cellular bandssuch as 824-960 MHz or 1710-2170 MHz. Systems such as the WLAN orBluetooth™ may require tuning on substantially higher frequency bandssuch as those around 2.45 GHz or 5 GHz.

In addition to this conventional functionality, the tuning element isused in the embodiments itself as an antenna radiator. Thisfunctionality may be provided both in a non-cellular system, such as theBluetooth™ or wireless local area network (WLAN) and in cellularsystems.

An example of the operation of such an antenna device is illustrated bythe flowchart of FIG. 3. More particularly, in response to detection at100 that tuning of resonance modes of a portable device is needed, atleast one electrical dimension of a ground plane of the electronicdevice can be optimised at 102 by tuning function provided by a combinedtuning and antenna radiator device. Radio signals can then becommunicated after the tuning operation by the tuned electronic deviceat 104.

The dual functionality of a tuning element and a radiator device can beachieved by suitable design of the structure thereof. The sharing of thetwo functions can be achieved in a frequency domain. That is, the tuningelement tunes the chassis electrical length into a different frequencyband(s) than where it is used as a radiating antenna element. Anappropriate separator such as a radio frequency (RF) filter can be usedfor achieving this, in situations where this is necessary.Alternatively, in certain applications the sharing of the functionalitycan also be done through multiplexing in the time domain with help of RFswitches. The separator may also be a combination of a filter and a RFswitch.

An example is now discussed in more detail with reference to FIGS. 4 to6 where a possible combination of a chassis choke for a 1800 MHzcellular band and an antenna for WLAN 2.45 GHz system is shown. It isnoted that the exemplifying dimensions and frequencies are only gives soas to ease the understanding of the invention and are not intended aslimitations of any kind.

The antenna element for non-cellular wireless system may be provided byan inverted-F antenna (IFA) or a planar inverted-F antenna (PIFA), orany modifications thereof. It is noted that the examples given in thisdescription are not limited to PIFA and IFA antenna types only. Instead,any other type of antennae may also be utilised.

The platform 30 where the combination of a chassis choke and an antennais implemented may be, for example, provided by a h1=100 mm*I=40 mmchassis, having a dual-band (900/1800 Mhz) PIFA 32 (h=6 mm) at its oneend. A RF feed 44 for 900/1800 MHz and a short circuit point 42 areprovided at that part.

A combined 1.8 GHz chassis choke and 2.45 GHz antenna device 36 is alsoprovide. The combined device 36 can be used to shorten the electricallength of the chassis down from the physical length h1=100 mm so thatthe effective electrical length thereof becomes approximately h2=70 mm.This length is close to an optimal chassis length for 1800 MHz.

A part of the tuning element structure may be separated from theoriginal structure with an RF filter 34. This separated part is denotedby L3 in FIG. 6.

The needed low-pass or band-stop response can be implemented e.g. by anLC-circuit. The chassis choke may be a grounded or shorted quarter-wavemetal strip at 1800 MHz. In practice the physical length thereof can beless than a quarter-wave. One end of the choke may be short-circuited at40 to the chassis edge while its other end can be left open. The chassischoke may be bent around the chassis corner, to get the open end to thedesired distance from the top of the chassis, as shown ein FIG. 5. TheRF currents near the 1800 MHz frequency see a high impedance level onthe edge of the chassis at around 70 mm distance from the top and arethus effectively choked. As a consequence, the RF currents at 1800 MHzsee effectively about a 70 mm long chassis and this part of the chassisis in half-wave resonance at 1800 MHz since 70 mm is about 0.4λ₀ at 1800MHz. It is noted that similar effect can be provided by other mechanismsas well. For example, a N*quarter-wave long choke may be used, where Nis an odd integer, may also be used.

The length of the full tuning structure is denoted by L1 in FIG. 6.Because of the filter, the RF currents at 2.45 GHz effectively areapplied only to a part of the full structure that is before the filter34. This length is denoted by L2 in FIG. 6. The length L2 is dimensionedso that it forms a resonance at around 2.45 GHz. An RF feed 38 of the2.45 GHz transceiver system is positioned at an appropriate distancefrom the short-circuit point 40. Thus, effectively an Inverted-F Antenna(IFA) is formed for 2.45 GHz band.

If needed, the 2.45 GHz RF feed can be electrically separated from thestructure at 1800 MHz band e.g. by another filter. The distance betweenthe RF feed point and the short-circuit point can be configured suchthat a suitable impedance matching can be obtained for the 2.45 GHzsystem. The location of the short circuits can be common for both thechassis choke and the WLAN antenna functionality.

The suitable lengths of L1 and L2 for obtaining suitable resonances forchoke operation and for antenna operation may also depend on the type ofa filter that is used and the implementation thereof. For example, if anLC circuit is used for the filter, the lengths L1 and L2, and the valuesL and C can be adjusted to achieve suitable resonances for bothfunctionalities.

A chassis choke configuration may include a pair of chassis chokes. Oneof the chokes may be provided on one edge of the chassis and the othersymmetrically on the opposite edge. A wireless local area network (WLAN)antenna functionality can be implemented to only one or both of thechassis chokes. If the WLAN antenna functionality is implemented to bothof them, they can be used as a diversity antenna system. Alternatively,an antenna radiator for some other band, such as 5 GHz band, can beimplemented within the second choke.

In an embodiment shown in FIG. 7 the physical length of a choke 50 canbe decreased by integrating an inductor 52 of a suitable inductancevalue within the choke structure to increase the electrical length ofthe choke. For example, this can be provided by a lumped component or aPWB implemented inductor using a microstrip, a stripline or similararrangement. Although the inductor is used in the choke to increase theelectrical length of the choke, the choke itself is used to decrease theelectrical length of the chassis. This provides a possibility to have achoke that may not need to be bent around a corner of the chassis. It isnoted that similar effect can be provided by other mechanisms as well.

Furthermore, it is possible to implement a reconfigurable chassis chokeconfiguration where a suitable inductor may automatically be selectedfrom a few different inductors with help of an RF switch system. Thisenables a chassis choke of suitable length for different needs. Forexample, an appropriate choke can be provided for different frequencybands, different operational states in e.g. fold or sliding devices.This kind of reconfigurable chassis choke system may also be used as achassis loading element at certain frequency band, if needed.

In a chassis choke configuration provided with two or more chokes, thelength or the shape of the chokes may intentionally be designeddifferently. This may be used to further broaden the bandwidth. In animplementation where a lumped inductor is used within the chokes,different inductor values can be chosen in the design of the two chokesto give the same benefit.

A further example will now be described wherein a combination of achassis loading element for 900 MHz cellular bands and an antennaradiator for a non cellular 2.45 GHz system is provided. The startingpoint platform can be the same as in the example above, i.e. a portableelectronic device where one end of a for example 100 mm*40 mm chassis isprovided with a dual band PIFA. At the other end there is a chassisloading element 54 that is connected to the chassis 30 through aninductor 56, see FIG. 8. The chassis loading element may be configuredsuch that it functions as a passive element that increases theelectrical length of the chassis or the electrical length of the groundplane in a desired frequency band. The purpose is, for example, to lowerthe first resonance of the 100 mm long chassis, to get it closer to the824-960 MHz band.

FIG. 9 shows a further example of a chassis tuning slot 58. A lumpedelement 59 such as an inductor or a capacitor, or a filter may beprovided in the slot for separating the two sides of the slot.

FIG. 10 shows an example of a chassis tuning or loading plate 60. Aninductor, a capacitor, a filter or the like may be provided at 62 in theslot 61 for separating the chassis 30 and the chassis loading plate 60(a segmented part of the chassis). A difference to the FIG. 8 example isthat here a part of the ground plane is separated from the chassis toprovide the loading plate.

A conventional version of the chassis loading element is passive, i.e.no RF feed is connected to it. In an advanced version an RF feed may beattached, for example for a 2.45 GHz system. One part of the loadingelement is separated from the main part of the structure with a filterso that a resonance can be achieved for 2.45 GHz antenna functionality.

In accordance with a further example a combination of a chassis loadingelement for 800-900 MHz cellular bands and an ultra wide band (UWB)monopole antenna for 6-8 GHz may be provided.

In accordance with a yet further example a combination of a chassistuning slot for 800-900 MHz and 1800 MHz cellular bands and a slotantenna for 2.45 GHz system may be provided.

The above configuration may be designed by using a tuning element as thestarting point of a design and add an antenna radiator functionality ontop of it by a suitable design. The tuning element may operate in alower frequency band than the desired antenna radiator functionality. Inthis case the dimensions of the original full structure of the tuningelement do not need to be increased when adding the antennafunctionality. It is also possible to design a configuration where thetuning element operates in a higher frequency band than the desiredantenna radiator functionality.

The configuration can also be provided also other way around, i.e. thestarting point can be an antenna radiator to which a tuningfunctionality is then added by means of a suitable configuration. Inthis case the primary functionality of the combined structure is theantenna radiator and the tuning functionality is an add-onfunctionality. Such approach can be employed in configuration examplesas discussed below.

In accordance with an example a higher band cellular antenna is employedas a chassis tuning element for a lower band cellular antenna. In thisexample a low band (824-900 MHz) cellular antenna may be located at oneend of a monoblock chassis. A high band (1700-2000 MHz bands) cellularantenna is located at the opposite end of the chassis. A switch (andpossibly an additional switchable inductor) is incorporated into thefeed structure of the high band cellular antenna so that it can also beused as a chassis loading element for increasing the electrical lengthof the chassis seen by the lower cellular bands. The low and highcellular bands are not used simultaneously so this kind of switchingbetween the functionality as a high cellular bands antenna and a chassistuning for low cellular bands is possible.

In accordance with another example a part of the structure of a largeinternal antenna of a cellular phone may be utilized as a chassis tuningelement. For example, an internal antenna for frequency modulation (FM)or an internal antenna for DVB-H system can be employed as a chassistuning element for an 800-900 MHz cellular band. An internal FM antennamay have a long radiator wire that is used as a receiving FM antennaelement. A part of the FM antenna element structure may be separatedwith a suitable filter or switches and be utilized as a chassis tuningelement e.g. for cellular 900 or 1800 MHz bands. The FM antenna elementand the tuning functionality may be co-designed. For example, theradiator wire of the FM antenna element is routed inside the cellularphone plastic covers in such a way that a part of the wire can beadvantageously utilized to increase the chassis electrical length seenby the cellular bands.

The above examples were presented in view of monoblock chassis. However,similar principles can be applied also for other mechanical forms ofmobile devices such as the foldable and slideable devices shown in FIGS.2 a and 2 b. Adaptive chassis tuning may be used in fold phones andslide phones, or generally in any portable device having multiplemechanical operation states. The device can be configured to detect themechanical state it is, and then to tune the chassis length or otherdimension differently. For example, a fold phone may be electrically tooshort when it is closed. At this state the electrical length can beincreased, for example by any of the ways explained above. On the otherhand, in the open state, the effective chassis may be too long. In thisstate it is appropriate to reduce the effective length.

In the examples above the antennas were implemented as self-resonatingantennas. The examples were given with IFA and PIFA type of antennas.Some other resonating antennas such as microstrip loop antennas may alsobe used. The invention is not limited to self-resonant antennas butnon-resonant coupling element type of antennas that are matched with amatching circuit can be used.

A tuning element can also be provided by means of a combination of anyof the tuning elements discussed above, or utilize a chassis tuningtechnique not especially mentioned here.

A tuning element may be configured to tune at least one electricaldimension of a ground plane, for example, one of the dimensions, eitherlength or width, of a printed wiring board (PWB). A printed wiring boardis typically used to form the ground plane of the antenna system withina portable electronic device. The printed wiring board is typicallyutilised for several functions, one of which is to provide the groundplane for the antenna system by using some of the layers within amultilayer printed wiring board as solid copper etched metallicsurfaces. These surface(s) usually cover the entire, or the majority, ofthe surface of at least one layer of a multilayer printed wiring board.This can be used to maximise the flow of current in the ground plane,which in turn maximises the performance of the antennae in most cases.The ground plane may also provide a key radiating element within theantenna system.

In addition of being provided as a separate component, the ground planemay also be embedded in a cover of a portable electronic device or maybe provided to form a part of the housing of the portable electronicdevice.

One implementation of the antenna functionality of a tuning elementcould be such that the feeding RF signal to (or from) the tuningelement, when it is used as a radiating antenna element, is couplednon-galvanically e.g. by aperture-coupling techniques.

Another possible implementation is where the tuning element is used as aparasitic radiator for a nearby antenna. In this application the tuningelement primary function is to tune the chassis electrical length in afrequency band A. Its secondary function is to act as a parasiticradiator in a frequency band B. In this case no RF feed line isconnected to the tuning element but an RF feed is connected to a nearby,driven antenna. The parasitic radiator function of the tuning elementthen increases the bandwidth of the nearby antenna at some desiredfrequency band.

It is noted that the term antenna radiator used in this document mayrefer to an antenna element either for a transmitter system, or areceiver system, or a transceiver system. Accordingly, a radio frequency(RF) feed may refer to an input port of a transmitting system, an outputof a receiver RF system, or a input/output of a transceiver RF system.

A tuning element utilized in this invention may be applied to tune notonly the electrical length but more generally the electrical dimensionsof the chassis. Thus, in addition, or alternatively, some othergeometrical dimension of the chassis, in particular the width may betuned. Considering these two dimensions, the electrical length of thechassis usually dictates the longitudinal resonance modes and theelectrical width usually dictates the transversal resonance modes. Theelectrical width may be tuned in order to utilize the transversal modesas well. For example, in a “curved” chassis, there can be bothlongitudinal and transversal resonance modes, or combinations of them.

The tuning element functionality of the structure can be configured tooperate in a single or multiple frequency bands. A multiband tuningelement can tune the electrical size of the chassis optimally forseveral frequency bands simultaneously. In addition, the antennafunctionality of the structure can be designed to operate in one ormultiple frequency bands.

For example, a chassis choke may be provided that can be itself operateas a choke in two different frequency bands. A dual-band chokeconfiguration 64 that can be used as a chassis choke in certainembodiments is shown in FIG. 11. The configuration may be provided withinductors 66.

In a typical use scenario a tuning element can be used to tune theelectrical size of the chassis optimally for cellular bands. In otherimplementations a tuning element may be used to tune the chassisresonance modes optimally for a non-cellular frequency band(s) and beused itself as an antenna radiator in cellular bands.

A multiradio antenna system of a mobile terminal may include severalcombined tuning and antenna radiator elements, which are co-designed.This way, optimal utilization of antenna and chassis tuningfunctionalities could be achieved for several frequency bands and radiosystems.

It is also possible to implement two separate shorting points, or groundconnections, one for the choke and one for the antenna functionality.Although one shorting point is enough in certain applications, it may beuseful to have two, or more, in some other applications.

The performance of some of the embodiments has been tested. To ease thecomparison with a single function antenna radiator, an antenna elementwith a 900/1800 MHz PIFA on an untuned 100 mm*40 mm chassis and itsS-parameters magnitude response are shown in FIG. 12.

As a background for understanding the results shown in FIGS. 12 to 14,the S11 response is a measure of the quality of impedance match seen atthe feed to an antenna or RF circuit under test. Ideally one would wantto transfer 100% of the source power to the antenna or RF circuit.However, due to discontinuities, stray inductances and straycapacitances in the physical structures associated with the physicalimplementation of the device and it's associated components, 100% powertransfer is only rarely achieved. This is also termed as Return Loss,measured in dB (decibels). In the test, a RF signal (source) across arange of frequencies is applied to the antenna or RF circuit under test(load), at a set power level, and the amount of signal (power) receivedback from the load is expressed as a power ratio, when compared with thesource power. The power received back is typically referred to asreflected power. When there is a large return loss (dB) then there issaid to be a “good match” over a given band of frequencies. For example,if there is a 10 dB return loss then 90% of the applied signal istransferred to the device, 10% is reflected, this being an “excellentmatch”. If there is a 6 dB return loss then 75% of the applied signal istransferred to the device, 25% is returned to the source. If there is a3 dB return loss then 50% of the power would be transferred and 50%reflected. And as a final example, if there is a 1 dB return loss thenonly 25% of the power would be transferred and 75% reflected, hence a“poor match”. From this test it is also possible to see where, forexample, an antenna is resonant.

From FIG. 12 it can be seen that at 1800 MHz band there is only oneresonance response. This originates from the 1800 MHz branch of theplanar inverted-F antenna (PIFA) element.

FIG. 13 illustrates the effects of introduction of a chassis choke. Ascan be seen, this leads to the first effective half-wave resonance ofthe chassis advantageously move close to 1800 MHz. Effectively, thisleads to a dual resonant response of S11. In FIG. 13 diagram the firstresonance originates from the PIFA and the second resonance originatesfrom the tuned chassis. It is noted that this example is based on arelatively rough optimisation, and that with more optimisation of theresonance couplings better results might be expected. Nevertheless, itcan be seen that the use of a combined tuning and radiator elementclearly improves the bandwidth of the device.

If so desired, the tuning element of this example can also be operatedas a WLAN 2.45 GHz antenna with a sufficient bandwidth. This is shown inFIG. 14.

The exemplifying embodiments described how an additional functionalitymay be integrated to an electrical size tuning element of acommunication device. This may result in effects such as savings inspace and cost. In a particular embodiment, a functionality of one ormore non-cellular antenna radiator element(s) is combined within achassis tuning element. This may be advantageous in antenna designs formultiradio and other communication devices. For example, reuse of achassis electrical size tuning element e.g. as a non-cellular antennamay reduce the total volume of a multiradio antenna system. This mayhelp in reducing the total volume of the overall product. Also, as thereare only a limited number of suitable locations for antennas and tuningelements in a mobile terminal, a more optimal use of these locations canbe achieved by combining an antenna with a chassis electrical lengthtuning element. There might not even be enough space for implementing achassis tuning element, if it is not integrated with some otherfunctionality. As a result of the present invention, better exploitationof mobile terminal chassis resonance modes and their control techniquescan be achieved.

It is noted that whilst embodiments have been described in relation towireless communication devices such as mobile terminals, embodiments ofthe present invention are applicable to any other suitable type ofapparatus suitable for communication via a wireless interface. It isalso noted that although certain embodiments were described above by wayof example with reference to the exemplifying standards, cellularnetworks and wireless local area networks, embodiments may be applied toany other suitable forms of wireless interfaces than those illustratedand described herein. It is also noted that the term wireless isunderstood to refer to any radio interface that an apparatus configuredfor wireless communication may use.

It is also noted herein that while the above describes exemplifyingembodiments of the invention, there are several variations andmodifications which may be made to the disclosed solution withoutdeparting from the scope of the present invention as defined in theappended claims.

The invention claimed is:
 1. An antenna device for a portable electronicdevice configured to provide in a combination a tuning element fortuning at least one electrical dimension of the portable electronicdevice and an antenna radiator element of the portable electronicdevice.
 2. An antenna device as claimed in claim 1, wherein the tuningelement is configured to tune at least one electrical dimension of aground plane of the portable electronic device.
 3. An antenna device asclaimed in claim 1, wherein the ground plane comprises a printed wiringboard.
 4. An antenna device as claimed in claim 1, wherein the groundplane is embedded in at least one of a cover of the portable electronicdevice or is provided as a part of the housing of the portableelectronic device.
 5. An antenna device as claimed in claim 1, whereinthe tuning element is configured to tune the at least one electricaldimension of the portable electronic device so that the resonancethereof is substantially optimal on at least one given frequency.
 6. Anantenna device as claimed in claim 1, comprising at least one separatorfor separating the functions of the tuning element and the antennaradiator element.
 7. An antenna device as claimed in claim 6, whereinthe at least one separator comprises at least one of at least one filterand at least one radio frequency switch.
 8. An antenna device as claimedin claim 1, wherein the tuning element comprises at least one of a slot,wavetrap, grounded microwave element or loading element.
 9. An antennadevice as claimed in claim 1, wherein the at least one electricaldimension comprises at least one of an electrical length and electricalwidth.
 10. An antenna device as claimed in claim 1, wherein the at leastone electrical dimension comprises at least one dimension of at leastone of a chassis, a ground plane and printed wiring board of theportable device.
 11. An antenna device as claimed in claim 1, whereinthe tuning element is configured to change an electrical dimension ofthe portable electronic device.
 12. An antenna device as claimed inclaim 1, wherein the tuning element and the antenna radiator elementoperate on different frequency bands.
 13. An antenna device as claimedin claim 1, comprising at least two chokes.
 14. An antenna device asclaimed in claim 13, wherein at least one of the length or shape of theat least two chokes is different.
 15. An antenna device as claimed inclaim 13, comprising lumped inductors with different inductor valueswithin the at least two chokes.
 16. A portable electronic devicecomprising an antenna device configured to provide in a combination atuning element for tuning at least one electrical dimension of a groundplane of the portable electronic device and an antenna radiator elementof the portable electronic device.
 17. Portable electronic device asclaimed in claim 16, wherein the portable electronic device isconfigured to detect operational state thereof and the antenna device isconfigured to be responsive to a detected operational state.
 18. Amethod in a portable electronic device, comprising tuning at least oneelectrical dimension of the portable electronic device by a combinedtuning and antenna radiator device; and communicating radio signals viathe tuned portable electronic device.
 19. A method as claimed in claim18, comprising tuning the at least one electrical dimension of theportable electronic device so that the resonance thereof issubstantially optimal on at least one given frequency.
 20. A method asclaimed in claim 18, comprising changing an electrical dimension of theportable electronic device.